Arrangement for controlling regulatable pumps

ABSTRACT

A cylinder housing is provided in its inner circumferential surface with a groove, and a control piston is slidable in the housing to opposite sides of a center position and is provided with a pair of axially saced grooves in its outer periphery which, when the piston is in center position, are located at opposite axial sides of the groove in the inner surface of the cylinder housing. A side member is guided in a stepped bore of the piston for axial sliding movement relative thereto and defines with the piston two pressure chambers each of which communicates with one of the outer grooves of the piston, and each of the chambers is provided with a relatively small port connecting it with a pressure fluid venting conduit.

limited States Patent [1 1 Martin July 3, 1973 [54] ARRANGEMENT FORCONTROLLING 3,677,138 7/1972 Goscenski 91/378 REGULATABLE PUMPS IPrimary Examiner--William L. Freeh [75] lnvemor' ggfg z HarsewmkelAssistant Examiner-Gregory LaPointe y Attorney-Michael S. Striker [73]Assignee: Gebr. Claas, l-larsewinkel ub'er Gutersloh, Germany [57]ABSTRACT [22] Filed: Sept. 27, 1971 A cylinder housing is provided inits inner circumferen- Appl. No.: 184,095

tial surface with a groove, and a control piston is slidable in thehousing to opposite sides of a center position and is provided with apair of axially saced grooves in its outer periphery which, when thepiston is in center position, are located at opposite axial sides of thegroove in the inner surface of the cylinder housing. A side member isguided in a stepped bore of the piston for axial sliding movementrelative thereto and defines with the piston two pressure chambers eachof which communicates with one of the outer grooves of the piston, andeach of the chambers is provided with a relatively small port connectingit with a pressure fluid venting conduit.

IMENIEUJUL3 m rs sum 2 or 2 1/ Eu r ARRANGEMENT FOR CONTROLLINGREGULATABLE PUMPS BACKGROUND OF THE INVENTION The present inventionrelates generally to control arrangements, and more particularly tocontrol arrangements for controlling regulatable pumps. Still moreparticularly the invention relates to an arrangement for controlling aregulatable hydraulic pump, particularly but not exclusively an axialpiston pump.

It is already known to provide axial piston pumps in which the pistonstroke is to be continuously regulatable in both directions of movement,that is of feed. This is accomplished, according to the prior art, via acontrol motor or arrangement having a control piston which precisely andimmediately follows the movements of an associated manually adjustablecontrol slider which is normally maintained in zero setting position byspring elements. The zero setting position can be temporarilycontrolled, independently of the manual control, by automaticallyoperating devices in the region of the center position of the controlpiston, in order to obtain exact fixing of the center position of thecontrol piston and thus of the zero setting position of the pump.

German Pat. No. 1,601 ,701 discloses an arrangement of this generalcharacter which affords precise centering of the control piston inautomatic manner. The control piston operates as a differential pistonwith the piston rod being configurated as an additional control member.The actual slide member in this construction is connected with anactuating rod with a predeter mined axial play, which axial rod isprovided with control surfaces and control bores in order to obtainfixing of the center position of the control piston. It has been found,however, that this prior-art construction is economically not wellfeasible because it is rather complicated in its construction andtherefore expensive in its production. Also, such a construction isoperable only when the control piston is configurated as a differentialpiston, and in order'to control the piston it is necessary to use oilfrom the main pressure oil circuit, requiring the provision ofadditional devices which act as force amplifiers when the control pistonis to be moved out of its exact center position in which the pump is inzero setting position and no oil is passed through the main circuit. I

SUMMARY OF THE INVENTION It is, accordingly, a general object of thepresent invention to overcome the aforementioned disadvantages of theprior art.

More particularly it is an object of the invention to provide anarrangement of the general type here under discussion which is notpossessed of the disadvantages attendant to the prior art.

A concomitant object of the invention is to provide such an arrangementwhich is very simple in its construction and therefore to produce, andwhich fulfills the requirements made of it in wholly satisfactorymanner.

In pursuance of the above objects, and of others which will becomeapparent hereafter, one feature of the invention resides, brieflystated, in an arrangement for controlling regulatable pumps, especiallyaxial piston pumps having continuous adjustment of the piston stroke inboth directions, according to which a combination is provided of acylinder housing having an inner circumferential surface, and a controlpiston slidable in the housing to opposite sides of a center position.The invention further provides an inner groove in the surface of thecylinder housing, being positioned to coincide with the center positionand in communication with the source of pressure fluid. A pair ofaxially spaced outer grooves encircle the piston and are located atopposite axial sides of the inner groove when the piston is in itscenter position. A slide member is guided in the piston for axialsliding movement relative thereto and defines therewith two pressurechambers each communicating with one of the outer grooves. A pair ofrelatively small ports are provided, each connecting one of the chamberswith a pressure fluid venting conduit.

In order to assure that despite exact center position of the controlpiston, and thus zero setting position of the pump which is beingcontrolled, the function of the arrangement is fully effective, thearrangement is connected in the feed circuit of a pump which supplies orreplenishes pressure fluid lost as a result of leakage.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammaticlongitudinal section through one embodiment of the invention;

FIG. 2 is a section similar to FIG. 1, taken in a plane at right anglesto that of FIG. 1 and omitting details exteriorly of the device andwhich are the same as in FIG. 1; and

FIG. 3 is a view similar to FIG. 2 but illustrating a further embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail, and firstly the embodiment which is illustrated in FIGS. l and2, it will be seen that reference numeral ll has been utilized todesignate the regulatable pump which is to be controlled. Such pumps arealready known per se and require no detailed discussion. The regulatingdevice for the pump l is identified with reference numeral 2 and ismoved or maintained against movement by the control piston 7, via alinkage 3, a connecting member 4, a pivot 5 and a member 6.

As the drawing clearly shows, the control piston 7 is slidablyaccommodated in a cylinder housing 8 and is provided with an axialstepped bore which in turn accommodates a slide member 9, a dishedspring lit) and dish springs 11. A replenishing pump 12 suppliespressure fluid, for instance oil, via the conduits l3 and 14 to theone-way valves 15, via which leakage oil or oil which is used in themain fluid circuit, is replenished. In addition the pump 12 supplies oilvia the conduit llfi, the bore 19, the longitudinal groove 20 and thebore 21 into the control chamber 22 which is defined between or by themembers 7 and 9. Excess oil supplied by the pump 12 flows via conduitsl3 and 14, and via the pressure-limiting valve 23 into the oil reservoir36.

FIG. 1 also shows that the slide member 9 is provided with cylindricalcontrol surfaces 24 and 25 which close the bores 26 and 27 in the centerposition, and that the member 9 is further provided with cylindricalrecesses 28 and 29 which are connected via bores 30 and 31 of the centerbore 32 in the member 9, free space 33 in the piston 7, bore 34 andconduit 35 with the reservoir 36.

It will be appreciated that if for instance a force acts on the member 9in the left-hand direction in the drawing, and if this force is greaterthan the force exerted by the spring 11, the member 9 will shift towardsthe left in and with reference to the piston 7. As a result of this thecontrol surface 24 opens the bore 27 so that oil under pressure can'flowthrough the bore 27 ahead of into the chamber 37. At the same time, oilcan flow from the chamber 38 via bore 26 into the chamber 29, and fromthere through bore 31 and bore 32 into the free space 33, from where itexits via bore 34 and flows via conduit 35 into the reservoir 36. As aresult of this, the piston 7 will move towards the left-at the same timeactivating the regulating device 2 of the pump luntil the left-handforce acting upon the member 9 terminates.

In accordance with the invention, and attention is now particularlydirected to FIG. 2, the inner circumferential surface of the cylinder 8is provided with an inner groove 39 and which is connected with theconnection 19 of the pump 12 so that it is continuously under pressure.A control surface 40 provided on the piston 7 closes the groove 39 andis delimited at opposite lateral sides by the outer grooves 41 and 42provided in the piston-7. The width of the groove 39 and of the grooves41 and 42 is determinative of the length of the path required for thecenter position return.

When the piston 7 moves from the left-most position it assumes, backtowards the center position, it can stop in any position and remainthere without being arrested, until the right-hand edge bounding thegroove 41 has moved beyond the left-hand edge bounding the groove 39.Thereupon, that is when this takes place, oil under pressure flows fromthe groove 39 into the groove 41, and from there through the channel 44into the pressure chamber 45. It thus forces the member 9 in the piston7 to move towards the right until the dished springs abut. As a resultof this the piston 7 itself moves farther towards the right in thehousing 8 until the control surface 40 closes the groove 39 and thesupply of oil out of the groove 39 is terminated. The pretension springs11 press the member 9 with the spring to its center orzero settingposition, and oil in the chamber 45 escapes through the groove 49 intothe space 28 and from there into the reservoir 36. The groove 49 could,of course, be omitted if the bead of the member 9 were to beaccommodated in the bore of the piston 7 with greater play thanillustrated.

The embodiment illustrated in FIG. 3 is largely the same as that inFIGS. 1 and 2, and any extraneous componentssuch as the pump 1, thedevice 2, etc.- which are shown in FIG. 1 have not been included in FIG.3 because they should be understood as being the same as in FIG. 1. Theembodiment in FIG. 3 in fact differs from that in FIGS. 1 and 2 only inthat the pressure chambers 45a and 46a in this embodiment are notdelimited by the actual bore accommodating the member 9, but instead bythe walls oflarger bores which are provided at opposite ends of the borefor the member 9 and which accommodate pistons closing the chambers 45aand 46a. The bores from the grooves 410 and 42a to the chambers 45a and46a are arranged analogously to those illustrated in FIG. 2, and theoperation of the embodiment in FIG. 3 is the same as that in FIGS. 1 and2.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in anarrangement for controlling regulatable pumps, it is not intended to belimited to the details shown, since various modifications and structuralchanges can be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended 1. In an arrangement for controllingregulatable pumps, particularly axial piston pumps having continuousadjustment of the piston stroke in both directions, in combination, acylinder housing having an inner circumferential surface; a controlpiston slidable in said housing to opposite sides of a center position,said piston defining at its opposite axial ends a first and a secondfluid chamber; an inner groove in said surface, positioned to coincidewith said center position and in communication with a source of pressurefluid; a pair of axially spaced outer grooves encircling said piston andlocated at opposite axial sides of said inner groove when said piston isin said center position; a slide member guided in said piston for axialsliding movement relative thereto and defining therewith two pressurechambers each communicating with one of said outer grooves; a pair ofrelatively small ports each connecting one of said chambers with apressure-fluid venting conduit; and passage means communicating with therespective fluid chambers and controlled by said slide member so that,when said slide member moves towards said first chamber the pressure offluid in the latter drops and the pressure of fluid in said secondchamber increases, and vice versa.

2. In an arrangement as defined in claim 1; further comprising apressure-fluid chamber in said piston, and a pressure-fluid conduitcommunicating with said pressure-fluid chamber; and wherein said innergroove is located in the region of said pressure-fluid chamber.

3. In an arrangement as defined in claim 1; and further comprisingspring means biasing said slide member to a normal zero settingposition.

4. In an arrangement as defined in claim 1; further comprising areplenishing pump for replenishing leaked pressure fluid, and a pumpcircuit through which pressure fluid supplied by said pump passes; andwherein said cylinder and piston are interposed in said pump circuit.

5. In an arrangement as defined in claim 1, said piston having a steppedaxial passage, and said slide member being at least in part slidablyreceived in said passage.

1. In an arrangement for controlling regulatable pumps, particularlyaxial piston pumps having continuous adjustment of the piston stroke inboth directions, in combination, a cylinder housing having an innercircumferential surface; a control piston slidable in said housing toopposite sides of a center position, said piston defining at itsopposite axial ends a first and a second fluid chamber; an inner groovein said surface, positioned to coincide with said center position and incommunication with a source of pressure fluid; a pair of axially spacedouter grooves encircling said piston and located at opposite axial sidesof said inner groove when said piston is in said center position; aslide member guided in said piston for axial sliding movement relativethereto and defining therewith two pressure chambers each communicatingwith one of said outer grooves; a pair of relatively small ports eachconnecting one of said chambers with a pressure-fluid venting conduit;and passage means communicating with the respective fluid chambers andcontrolled by said slide member so that, when said slide member movestowards said first chamber the pressure of fluid in the latter drops andthe pressure of fluid in said second chamber increases, and vice versa.2. In an arrangement as defined in claim 1; further comprising apressure-fluid chamber in said piston, and a pressure-fluid conduitcommunicating with said pressure-fluid chamber; and wherein said innergroove is located in the region of said pressure-fluid chamber.
 3. In anarrangement as defined in claim 1; and further comprising spring meansbiasing said slide member to a normal zero setting position.
 4. In anarrangement as defined in claim 1; further comprising a replenishingpump for replenishing leaked pressure fluid, and a pump circuit throughwhich pressure fluid supplied by said pump passes; and wherein saidcylinder and piston are interposed in said pump circuit.
 5. In anarrangement as defined in claim 1, said piston having a stepped axialpassage, and said slide member being at least in part slidably receivedin said passage.